PROJECT SUMMARY/ABSTRACT Phonology (relating to the patterning of speech sounds) and morphology (relating to the formation of words) are known to interact cross-linguistically and in developing systems, and this phenomenon is referred to as morpho-phonology. For example, in English, the third-person singular morpheme -s is pronounced differently depending on the preceding sound: ?eat[s]? vs. ?see[z]? vs. ?kiss[?z]?. Typically-developing children show differing levels of accuracy on this morpheme, and this is attributable in part to the surrounding phonological context. This proposed research program will evaluate the influence of morpho-phonological interaction in the language of children aged 4 to 6 years with phonological disorder (PD), those with developmental language disorder (DLD), and those children with co-occurring PD and DLD (PD-DLD) through manipulation of phonological and morphological complexity in the selection of treatment target words. Experiment 1 will evaluate effects of phonological complexity on speech-sound generalization learning following treatment of children with PD and PD-DLD when targets vary with respect to morpho-phonological complexity. Experiment 2 will evaluate morpheme generalization learning following treatment of children with DLD and PD-DLD when targets vary by phonological complexity. The proposed research will 1) bridge linguistic theory with clinical treatment to identify ideal targets for generalization learning across populations, 2) focus on both morphology and phonology, which are known to interact in normal systems, and 3) define how these principles together can inform the management of disordered systems. Upon completion of the proposed work, the nature of morpho-phonological interactions within and across these clinical populations will be identified, and the role of morpho-phonological complexity in driving change following treatment will be delineated.